1. Field of the Invention
This invention relates to poster display systems and to methods of displaying poster images.
2. Description of Related Art
It is often desired to display more than one poster image at a particular site and there already exist poster display systems in which the poster image is displayed on a series of juxtaposed elongate elements of polygonal cross-section. One face of each element carries a respective part of the poster image and the image displayed can be changed by rotating all of the elements in unison so that they each present another face. Such display systems involve the use of a multiplicity of polygonal elements each of which must be rotated during use of the systems and to each of which must be attached respective parts of each poster image. Thus the manufacture of such a system is expensive and the changing of the set-up of the system to enable a different set of poster images to be displayed is cumbersome and expensive.
It has been proposed to provide a poster display system for presenting a plurality of different images by mounting a masking sheet over a poster image sheet and moving the masking sheet small distances relative to the poster image sheet. The poster image sheet is formed with a multiplicity of image strips with adjacent strips defining portions of different images. The masking sheet has alternate opaque and transparent strips so as to reveal selected ones only of the poster image strips. In one position of the masking sheet relative to the image sheet, strips of a first image remain exposed while other image strips are concealed behind opaque strips of the masking sheet. In another position of the masking sheet relative to the image sheet strips of the first image are concealed behind opaque strips whilst the image strips relating to another image that were previously concealed behind the masking strips become exposed. Provided the width of the masking strips is not too great, a human eye will fill in the masked parts of the image and see an entire poster image. The image seen will, however, vary according to which image strips are exposed. Thus the display system may be used to display a plurality of unrelated static images, or a plurality of closely related images which, when displayed in the correct sequence, provide an animation, as for example proposed in U.S. Pat. No. 3,918,185.
For the proper functioning of a poster display system of the kind just described, in which image strips relating to a plurality of poster images are provided on a common poster image sheet, it is very important that the relative positions of the poster image sheet and the masking sheet are very precise. That requirement applies and is relatively simple to meet if only two images are included on the poster image sheet but is more onerous if more images are included. Furthermore, it is very desirable that it should be easy to replace one poster image sheet by another so that a different set of images can be displayed by the system. Further still, it is very important that the poster image sheet and the masking sheet maintain overall contact with each other between the surfaces of the composite material upon which the grids are printed.